Polyurethane foam production involves metering and pumping of the resin and isocyanate ingredients, which are prepared as a number of liquid components or streams, to the mixer where they are mixed thoroughly and dispensed. A typical formulation comprises two streams consisting of the isocyanate and the resin. The resin stream is a mixture of polyols, crosslinking agent such as diethanolamine (DEOA), surfactant, catalyst, water, auxiliary blowing agents, and other possible additives.
Foams demonstrating good stability also exhibit improved, isotropic physical properties, and are more easily processed with existing equipment. More specifically, molded foams with good bulk, vent, and shear stability are characterized as having small, uniform cellular structure throughout the interior of the foam. Polyurethane foams with superior surface stabilization have a layer of fine cells adjacent to the outer surface of the foam. Foams that are dimensionally stable, typically also open-celled, exhibit a reduced tendency to shrink immediately after being removed from a mold. Non-molded flexible foams require good bulk stabilization and dimensional stability, which if not present will lead to foam collapse or densification. Reduced emissions of additives in flexible foam can lead to reduced fogging on interior automobile windshields.
In the past, chemical strategies for selecting formulation variables in order to optimize the bulk, shear, vent, surface and dimensional stability have been very successful for many applications. Key variables include the judicious selection of surfactants and catalysts. The foam industry now has changed their strategy to one of maintaining foam physical properties while at the same time reducing their raw materials and/or processing costs. Approaches include reducing density by using less wet chemicals or injecting liquid carbon dioxide, lowering the amount of relatively expensive graft copolymers, using blends of TDI/MDI, and incorporating isocyanate terminated pre-polymers. All of these approaches have placed increasing challenges on the accompanying additives which could not be fully met using known prior art.
Silicone surfactants used for the production of flexible polyurethane foams are typically polydimethylsiloxanes, organofunctional polydimethylsiloxanes or siloxane polyether copolymers.
U.S. Pat. No. 3,402,192 discloses polyoxyalkylene siloxane branch copolymers useful in the preparation of polyurethane foams.
U.S. Pat. No. 4,031,044 discloses siloxane-oxyalkylene copolymer surfactants as foam stabilizers for making polyether based high resilient flexible foam. U.S. '044 teaches a very broad class of structures, but the general class that is closely related to the present invention can be described by the formula EQU Me.sub.3 Si(OSiMe.sub.2).sub.x (OSiMeG).sub.y OSiMe.sub.3
wherein G is a group having the formula --D(OR").sub.m A wherein D is a divalent linking group such as an alkylene group, R" is composed of propylene groups and groups selected from the group consisting of ethylene and butylene groups wherein the amount of ethylene and butylene is less than 35 wt % of the total (OR") group, m has an average value from 1 to 15, and A is either an --OR', --OOCR' or --OOCOOR' group where R' is a group free of aliphatic unsaturation selected from the group consisting of hydrocarbon and hydrocarbonoxy groups. When the average value of x is 0-7, then y has an average value of 1-5; when x=0, y=1-5; when x=1 or 2, then y=1-4; when x=3 or 4, then y=1-3; when x is 5, then y is 1-2; and when x is 6 or 7, then y=1. See Example 7 for specific working embodiments.
U.S. Pat. No. 4,139,503 discloses the use of specific siloxane components at 0.01 to 2 g/100 g of polyol for the production of high resilience, open celled polyurethane foam. This patent only shows examples for polydimethylsilicones.
U.S. Pat. No. 4,347,330 discloses improved high resilience open celled flexible molded polyurethane foam by incorporating three cell modifiers consisting of a polysiloxane-polyoxyalkylene copolymer, a polymethylsiloxane, and a polyether polyol cell modifier containing polyoxyethylene groups in amount of at least about 80 percent by weight of the polyether polyol.
U.S. Pat. No. 4,690,955 discloses siloxane polyether copolymer surfactants with mixed hydroxy alkoxy capping for stabilizing molded flexible foam.
U.S. Pat. No. 5,633,292 discloses a method for the production of high resilience polyurethane foams using a surfactant containing alkyl substituents rather than alkoxy substituents.
The present invention involves the use of a certain narrow class of silicone polyether copolymers belonging to a specific structure range to provide improvement in flexible polyurethane foam stability.